Filtration of solutions is generally desired to remove particles in sample preparation applications, analytical techniques and prior to an instrumentation analysis, for example, or to sterilize a solution in tissue culture applications. Depending upon the volumes that need to be filtered, different syringe driven filter sizes, identified by their filter diameter, are available. These include 4 mm, 13 mm and 25 mm sizes. The 4 mm syringe driven filters are typically recommended for the filtration of volumes less than or equal to 1 ml.
Conventional syringe drive filters have male and female luer taper fittings designed to mechanically connect two medical devices such as a syringe and a needle. As shown in FIG. 1, most conventional syringe driven filters have a female luer lock inlet and male luer slip outlet. The female luer lock inlet ensures that the filter is securely (but removably) attached to the outlet of the syringe so as to prevent leakage and loss of sample while filtration takes place. This is especially critical when low sample volumes are being filtered. The lock is conventional and includes outer annular wings designed to be removably engaged (by twisting) in corresponding thread-like ribs in the outlet portion of the syringe. The internal diameter of the female luer is standardized, according to ANSI specifications, to receive a corresponding standardized male luer such as on a syringe. This standardization ensures that the male and female portions will properly mate. As an alternative to the luer lock design, a friction fit ("luer slip") can be used, especially in low-pressure applications.
Similarly, the male luer slip outlet on the syringe driven filter device allows, for example, a needle to be attached to the outlet of the filter and facilitates a direct injection of a filtered sample into an HPLC (high pressure liquid chromatography) instrument, for autosampler vials or other receptacle for further analysis.
Another conventional syringe driven filter device is illustrated in FIG. 2. This device includes a narrowed outlet or "recorder taper" used in place of the male luer slip of the device of FIG. 1. The recorder taper is narrower than the male luer slip, and thus does not function as a luer (i.e., it does not allow for a friction-fit engagement with a standardized female luer). However, the recorder taper facilitates filtration into small receiving vessels such as HPLC autosampler vials, vial inserts and the wells of microtitre plates. The smaller outlet further minimizes the potential of the filtered sample becoming lodged ("airlocked") through capillary action in the top of the narrow receiving vessel such as an autosampler insert, as the air caught beneath the sample cannot escape to allow the sample to flow to the bottom of the vessel. An additional feature of this design is a very small downstream (internal volume after the membrane) volume attributed to a smaller internal diameter in the outlet. This can be especially important with small sample volumes.
A still further conventional design is shown in FIG. 3. This design is a 4 mm syringe driven filter with a "tube tip" or "tube outlet". A short tube is inserted into the outlet orifice of the standard male luer slip design in order to facilitate the filtration into a small receiving vessel. However, this design suffers from the drawback of having a larger downstream volume by virtue of the length of the tube tip, which is undesirable with small sample volumes.
It therefore would be desirable to provide a filter device such as a syringe driven filter that includes all of the features of conventional devices, but does not suffer from any of their drawbacks.
It further would be desirable to provide a filter device that has multiple outlet features so that a single device can serve multiple laboratory filtration applications, thereby reducing the number of specialized filters the user needs to have on hand.